1. Field of the Invention
This invention relates to an automobile weight sensor for detecting the presence of a person in a car seat, and in particular to a sensor that can detect the presence of an occupant using strain sensitive resistors and provide an electrical signal to control activation of an airbag.
2. Description of the Related Art
Automobiles are equipped with restraint systems, such as seat belts, and inflatable restraint systems, such as airbags, to improve passenger safety. In some situations, these safety devices can injure the occupants. For example, an occupant in the front passenger seat may be injured by deployment of an airbag, if the occupant is a baby or child. It is desirable to control the operation of the airbag according to the weight of a passenger for improved performance of seat belts and airbags. A device for measuring the weight of a passenger sitting on a vehicle seat is needed to prevent or modify the deployment of the airbag when the weight is less than a predetermined amount.
There have been a number of attempts to measure the weight of a seat occupant, all with significant disadvantages. For example load cells or strain gages have been used in a vehicle seat. One problem encountered in measuring the weight of a seat occupant is that the weight reading needs to be uniform when the vehicle is moving. When the vehicle travels around a curve or in a turn, the weight sensor cannot have a large change in its reading. In other words, the weight sensor needs to be somewhat insensitive to loads that are not in the vertical direction. The load cells of the prior art have suffered from giving false readings when subjected to side loads.
The seat weight sensor also needs to be manufactured at a low cost and must be able to withstand large loads. The sensor cannot be damaged by crash forces or other overloads. Prior art seat weight sensors have suffered from requiring an extensive redesign of the seat frame in order to be installed. It is desirable for a seat weight sensor to be installed in existing car seats with a minimum of changes to the existing seat design.
A current unmet need exists for a reliable, low cost, robust automobile seat weight sensor that is insensitive to off axis loads and that can be installed in a vehicle with a minimum of changes to the existing seat design.